Current conveyor circuits are relatively well-known devices Typically, a current conveyor circuit includes a Y terminal (a voltage-input terminal for second-generation current conveyor circuits, for instance), an X terminal (a current-input terminal), and a Z terminal (a current-output terminal). A reference voltage is applied to the Y terminal, and the reference voltage drives an ideally equal voltage at the X terminal. Further, a reference current may be driven through the current conveyor circuit, and an input current may be applied to the X terminal (i.e., a current is drained from the X terminal). The input current applied to the X terminal is preferably conveyed to the Z terminal, which is at a higher impedance level than the X terminal.
Current conveyor circuits may be used in a variety of applications. For instance, current conveyor circuits may be used to compare input currents. As an example, the Z terminal output current of a first current conveyor circuit may be compared to the Z terminal output current of a second current conveyor circuit. Based on a comparison of the respective output currents, the difference between the input current applied to the X terminal of the first current conveyor circuit and the input current applied to the X terminal of the second current conveyor circuit may be inferred (since the input current applied to the X terminal is preferably conveyed to the Z terminal).
However, there are limitations associated with current conveyor circuits, and with using current conveyor circuits to compare input currents. For instance, the input current applied to the X terminal will be accurately conveyed to the Z terminal only when the input current is much smaller than the reference current driven through the current conveyor circuit (e.g., 10× smaller). Hence, the input current applied to the X terminal of a current conveyor circuit and the output current conveyed to the Z terminal are usually small.
Because the input current applied to the X terminal and the output current conveyed to the Z terminal are usually small, comparing the Z terminal output current of a first current conveyor circuit to the Z terminal output current of a second current conveyor circuit may be problematic. As examples, detecting the current difference between the respective Z terminal output currents may be slow and inaccurate.
Additionally, the reference voltage applied to the Y terminal may not always remain constant. For instance, variations in temperature (or other processes, more generally) may cause the reference voltage to fluctuate. If the reference voltage applied to the Y terminal does not remain constant, then the overall functionality of the current conveyor circuit may be adversely affected. As an example, the input current applied to the X terminal may fluctuate. Needless to say, fluctuations in the input current applied to the X terminal of either the first or second current conveyor circuit may cause further problems in comparing input currents.